Energy metabolism deficits are prevalent in autism spectrum disorder (ASD) and other mental conditions; however, causes of this comorbidity remain a puzzle. Genetic studies strongly implicated Wnt/β-catenin signalling and its effector the TCF7L2 transcription factor in neurodevelopmental disorders, including ASD. On the other hand, TCF7L2 gene variants are the strongest risk factors for type II diabetes. In my presentation, I will show experimental evidence that TCF7L2, in addition to its functions in the metabolic tissues, regulates energy metabolism in the highly interconnected thalamocortical circuit. Furthermore, thalamic deficiency of TCF7L2 causes autism-like behaviours. To explore the potential link between brain energy metabolism and ASD, we fed Tcf7l2-cKO mice with ketogenic diet, which normalised brain energy metabolism and improved social interactions. We propose that ASD can originate from compromised energy metabolism in thalamocortical circuits, and ketogenic diet may ameliorate core ASD symptoms in patients with enhanced aerobic glycolysis.